With development in the network technique, it became possible to transmit/receive contents such as text data, image data, sound data, and video data via a network. The function of transmitting/receiving contents via a network is provided for not only a stationary terminal device such as a desktop computer but also a portable terminal device such as a cellular phone or PDA (Personal Digital Assistants). Such terminal devices each having the network connecting function are widely spread and the number of terminal devices is enormous.
Generally, transmission/reception of information via a network can be performed in short time and at low price. In addition, the number of terminal devices each having the network connecting function is enormous, that is, a large amount of samples can be easily collected. There is consequently a system of sending a questionnaire and collecting answers by using a network (Patent document 1).
Patent document 1: Japanese Patent Laid-Open No. 2002-15096.
When the number of answers to a questionnaire is large, generally, variations occur in the quality of the answers due to, for example, an answer including a typing error, an answer of a person who answers the questionnaire not-seriously and insincerely, and the like. Consequently, if the answers are used as they are for an analysis, an adverse influence is exerted on the result of the analysis.